Neogene silicic volcanic complexes in the greater Borgarfjörður eystri area, NE-Iceland, are the focus of a petrological and geochemical investigation. The region contains the second-most voluminous occurrence of silicic rocks in Iceland, including caldera structures, inclined sheet swarms, extensive ignimbrite sheets, sub-volcanic rhyolites and silicic lava flows. Despite the relevance of these rocks to understand the generation of evolved magmas in Iceland, the area is geologically poorly studied [c.f. 1, 2, 3].
The voluminous occurrence of evolved rocks in Iceland (10-12 %) is very unusual for an ocean island or a mid-oceanic ridge, with a typical signal of magmatic bimodality, often called “Bunsen-Daly” compositional gap [e.g. 4, 5, 6]. The Bunsen-Daly Gap is a long-standing and fundamental issue in petrology and difficult to reconcile with continuous fractional crystallization as a dominant process in magmatic differentiation . This implies that partial melting of hydrothermally altered crust may play a significant role. Our aim is to contribute to a solution to this issue by unravelling the origin, timing and evolution of voluminous evolved rhyolites in NE-Iceland.
We use a combined petrological, textural, experimental and in-situ isotope approach on a comprehensive sample suite of intrusive and extrusive rocks, ranging from basaltic to silicic compositions. We are performing major, trace element and Sr-Nd-Hf-Pb-He-O isotope geochemistry, as well as U-Pb geochronology and Ar/Ar geochronology on rocks and mineral separates. Zircon oxygen isotope analysis will be performed in conjuction with zircon U-Pb geochronology for further assessment of the role of processes such as partial melting of hydrated country rock and/or fractional crystallization in generating Icelandic rhyolites. In addition, high pressure-temperature partial melting experiments aim to reproduce and further constrain natural processes. Using the combined data set we intend to produce a comprehensive and quantitative analysis of rhyolite petrogenesis, and of the temporal, structural and geochemical evolution of silicic volcanism in NE-Iceland. The chosen field area serves as a good analogue for active central volcanoes in Iceland, such as Askja and Krafla, where interaction of basaltic and more evolved magma has led to explosive eruptions.
 Gústafsson (1992) PhD dissertation, Berlin University.  Martin & Sigmarsson (2010) Lithos 116, 129–144.  Burchardt, Tanner, Troll, Krumbholz & Gustafsson (2011) G3 12 (7), Q0AB09.  Bunsen (1851) Annalen der Physik und Chemie 159 (6), 197-272.  Daly (1925) Proceedings of the American Academy of Arts and Sciences 60 (1), 3-80.  Barth, Correns & Eskola (1939) Die Entstehung der Gesteine. Springer Verlag, Berlin.  Bowen (1928) The evolution of the igneous rocks. Princeton University Press.
2012. 1475- p.
22nd Annual V.M. Goldschmidt Conference in Montréal, Canada